1. Field of the Invention
The present invention relates to a biaxial actuator for operating a movable portion, which includes an objective lens for focusing a beam of light coming from a light source such as a semiconductor laser on the signal surface of an optical disk, in both a focusing direction and a tracking direction.
2. Description of the Related Art
In the prior art, an optical pick up device has been used as a means for reading out an information signal recorded on an optical disk or writing information on the disk by applying a beam of light to the signal surface of the disk which is being driven by a disk drive device.
This optical pickup device is equipped with a biaxial actuator. In the biaxial actuator, the beam of light emanating from a light source such as a semiconductor laser can be applied in focus to the signal surface of the optical disk precisely along the recording track, by displacing the objective lens, which is used for focusing the beam of light on the signal surface of the disk, in biaxial directions of the focusing direction and the tracking direction by a magnetic drive force.
This biaxial actuator of the prior art has a structure, as shown in FIGS. 1 and 2.
In FIGS. 1 and 2, the biaxial actuator is equipped with a movable portion 1 and a stationary portion 2. The movable portion 1 is so supported with respect to the stationary portion 2 by an elastic support mechanism, which is interposed between the two portions 1 and 2, as to follow a fluctuation due to the motion of the optical disk. The movable portion 1 is equipped with an objective lens L called the "read lens" and a lens holder 3 supporting the objective lens L.
The lens holder 3 of the movable portion 1 is supported by a leaf spring 4 for controlling the focusing operation of the elastic support mechanism. Specifically, the lens holder 3 is supported by one end of the leaf spring 4 through a tracking hinge 6 of the elastic support mechanism. The other end of the leaf spring 4 is fixed to a yoke 5 of the stationary portion 2.
In case the movable portion 1 is subjected to a tracking operation in the tracking direction TR, it moves on the pin of the tracking hinge 6. In case, on the other hand, the movable portion 1 is subjected to a focusing operation in the focusing direction FC, it is moved by the elastic deformation of the leaf spring 4.
Moreover, the movable portion 1 carries a balancer B thereon. This balancer B is provided for balancing the movable portion 1 in weight with the objective lens L in the two focusing and tracking directions.
However, the biaxial actuator of the prior art, as shown in FIGS. 1 and 2, may receive an impact in the direction of arrow X from a fixed location FL, if it is hit by the fixed location FL when assembled into an optical pickup device, for example. In this case, the leaf spring 4 will be buckled by that impact. This buckling is caused by the fact that a large clearance E exists between the balancer B and a stopper S of the yoke 5. Specifically, the movable portion moves beyond its working range and its elastic limit in the clearance E, if the impact in the direction X is applied thereto, so that the leaf spring is buckled.
As used in this context, the term "elastic limit" means the working range in which the focus supporting members may return to their original form after the focus supporting members are displaced by shock. When the actuator of the objective lens is dropped, the focus supporting members are moved. At this time, if the focus supporting members are moved or displaced to beyond their working range (or elastic limit) which is determined by the material of the focus supporting members, the focus supporting members cannot return to their original shape. Thus, the focus supporting members change their shape.